INT 21 - DR DOS v3.31+ - RUN ALREADY-LOADED KERNEL FILE
AX = 4B80h
DS:DX -> ASCIZ name of program to EXEC
ES = segment of PSP for kernel file
Return: only if call failed
Note: DR DOS uses this call after an AX=4B01h to load the kernel file into
memory and patch the program's parent-PSP field to point at itself
SeeAlso: AH=4Bh"EXEC"